Heretofore, a method for switchably displaying a plural number of messages on a cathode ray tube display apparatus by storing a plural number of messages in the regenerating buffer memory and providing an address signal designating a message from the computer or the external controller has been proposed (see, for example, Unexamined Published Japanese patent application No. 49-22823). In accordance with such a method, however, the memory must be rewritten whenever a part of the message displayed will be changed, and no scrolling can be made because the address signal designates a full message in a frame.
Another method for scrolling without rewriting the content of the regenerating buffer memory is to provide a row address table for storing the address information of the regenerating buffer memory in the displaying order, and to change the arrangement of the row address stored in the row address table (see, for example, Unexamined Published Japanese patent application No. 50-116238). In such a method, however, the content of the row address table must be rewritten each time of scrolling, so the efficiency is lowered.
Another method for not only switchably displaying messages on a cathode ray tube display apparatus but also achieving scrolling by providing a regenerating buffer memory of a capacity greater than the number of characters displayed on the CRT, storing the start address corresponding to a message displayed on the CRT among the contents of the regenerating buffer memory in a register, and reading out characters in a message starting at the start address from the regenerating buffer memory has also been proposed (see, for example, Unexamined Published Japanese patent Application No. 51-51243). Although this method can be used for switchably displaying a plural number of messages by changing the start address, and also for scrolling, characters to be displayed must be sequentially stored in the regenerating memory, so allocating of the memory is not made freely, and when there is a requirement to change a part of the content of a frame, the memory must be rewritten.